This invention pertains to a process for continuous production of sulfur crosslinked polymer asphalts, whereby said process makes it possible to produce all kinds of modified binders, from conventional binders such as are used today to highly concentrated polymer binders that do not yet exist.
Improving the properties of asphalts is today an absolute necessity in order to guarantee improved quality for the materials that use asphalts and to thus help to create and develop new applications. This goal is achieved by increasing the polymer concentration that said materials must assimilate. Unfortunately, few asphalts are truly compatible with polymers, and this incompatibility worsens as the quantity to be introduced into them is increased!
Today two families of polymer asphalts are available on the market:
a) physical mixtures that are produced by simple dissolution of polymers;
b) media that are transformed by a chemical reaction that is induced between components of the asphalts and polymer(s).
If these two discontinuous batch production processes are identical, the properties of the binders that are obtained by a chemical sulfur reaction, at equivalent polymer contents, are superior to those of binders that are produced from simple mixtures, both in terms of elastic performance and in terms of stability or storage under hot conditions. Nevertheless, for various reasons these two concepts do not make it possible to obtain highly modified binders. For no particular reason, where the dissolved-polymer contents can reach 9-10 percent for the majority of asphalts and, in the case of physical mixtures, from 5 to 6 percent polymer, solubility is quickly limited, and these mixtures decant in different phases under the action of an unavoidable phenomenon, which sets in more or less quickly over time. With sulfur-crosslinked asphalts, the polymer content also limits the ability to produce concentrated binders because in the liquid state, i.e., under storage conditions, several hours or several days after vulcanization complete and unstoppable polymerization takes place, leading to a gelatinous state, whereby this happens starting at 6 percent dissolved polymer. Thus, there are many new applications which these types of binders could offer but which have yet to see the light of day for the reasons cited above!
There is tremendous interest in this new process. These new, heavily modified binders will be very useful to the road-building industry, as well as to the field of sealants, and will make it possible to produce materials and coated materials that have very high levels of performance. The same will be true for the production of emulsions from these same binders: no such materials exist today.
Moreover, certain recovered plastics, rubber from discarded tires, and waste oils of mineral, vegetable, or synthetic origin can also be recycled within the framework of the binders produced by the invention.
These new innovative materials will be intended especially to be used to regenerate old coated materials on roads within the framework of the hot-recycling technique. Said innovative materials will promote the recovery, i.e., enhancement of the value, of old asphalt materials on roads and will keep them from being discarded.
From the economic standpoint, the advantages offered to road builders and sealant makers are numerous and can be mainly summarized as follows:
having binders whose performance is much better than that of the binders that are known today;
opening new avenues for techniques for building or maintaining roads at lower cost which, owing to their improved mechanical properties and exceptional fatigue strength, will help to improve the behavior and service life of roads significantly;
contributing to the practicability of emulsions and of the binders produced by the invention by the immediate and direct injection of product onto the feed heads of colloid emulsion mills, thereby opening the way to many new applications that can be provided by these truly special emulsions!
enhancing the value, in road and sealant applications, of certain waste products that today are for the most part destroyed, such as plastics, tire rubber, and lubricants, owing to the advantages offered by the vulcanization reaction that is employed in the invention;
recycling of all kinds of used asphalt materials by regenerating the contained asphalts through the incorporation of certain binders that are the direct result of the invention. The use of some of these crosslinked asphalts that have high polymer concentrations as a way to regenerate old coated materials may be done at a permanent coating facility or at a mobile facility that is outfitted in advance with the process. Depending on the characteristics of the materials that are to be recycled, just about 100 percent of them can be regenerated. This is due to the nature of the regeneration process that is employed within the heart of the old asphalt itself: the addition of plasticizing materials and polymers to the old asphalt structure which, under the crosslinking action of sulfur, will help, on the one hand, to reformulate a rejuvenated asphalt and, on the other, to create a polymer mesh that brings together all of the components. This will therefore be a modified-binder coated material that is obtained by this kind of recycling operation. This accounts for the bright prospects for obtaining, by using these products, recycled coated materials whose levels of performance are at least equivalent to, if not better than, the characteristics that they had at the time when they were first used.
For more than 25 years now, asphalts have been modified by the addition of polymers in order to improve their rheological properties and also to curb their ability to age. Two main effects are sought. The first is to increase the plasticity range in such a way that, under conditions of elevated temperature, the asphalt remains viscous enough that coated materials, as well as sheets of sealant complexes, are kept from deforming. The second effect, especially at low temperatures, is to reduce the rigidity of the material and to impart to it a great capacity for plastic deformation so that it will be able to withstand great stress.
Many families of polymers are currently used to add this type of modification to asphalt. Among these, the following can be cited: polyolefins, polyvinyl acetates or polyvinyl chlorides, elastomers, etc.. Of all these materials, it is elastomers that are best suited for imparting elasticity and, optionally, plasticity. As a matter of practicality, introduction of these polymers into asphalts is no simple matter. Specifically it is the morphological composition of the base asphalt, i.e., its groups of chemical components: saturated, aromatic, polar, and asphaltene, that dictate the choice of the polymer or polymers and limit-its or their solubility. For a particular type of asphalt, the level of modification that one can hope to achieve is more or less predetermined in advance.
With the exception of the sealant industries, which purchase so-called xe2x80x9cspecialxe2x80x9d asphalts, whereby they require that the materials delivered that they use be of an unvarying nature and composition in order to keep the quality of the plastic mixtures that are produced stable, refiners supply only so-called xe2x80x9crun-of-the-millxe2x80x9d asphalts in conformity with specifications. This is due to the organization of the petroleum markets and the technical and economic constraints imposed on refining. It is impossible for this industry to continuously produce a special type of asphalt. Because of the risks of segregation, attempts to introduce significant quantities of polymers have not succeeded in producing stable binders that are adapted to industrial use.
Chemically transformed asphalts obtained from styrene-butadiene (SB) of the statistical or stereo regulated block type, or tri-sequence styrene-butadiene-styrene (SBS), or styrene-isoprene (SI), or styrene-isoprene-styrene (SIS), or ethylene-propylene-diene (EPDM), or other types of polymers which have an unsaturated and a sulfur group in their chemical structures, make it possible to obtain, by using 30-50 percent less polymer, properties that are equivalent to those of binders that are-prepared by simple physical mixing. Owing to its high solubility, polymer SB is preferably employed in this kind of binder. Since this product is not, strictly speaking, a true polymer, it is its low molecular weight and the careful selection of the styrene/butadiene distribution that make it compatible with the full range of asphalts. Depending on the penetration of the asphalt, contents that may exceed 30 percent can be dissolved. On the other hand, without using the chemical reaction with sulfur, this material modifies the natural properties of the starting asphalt very little. Nevertheless, for contents on the order of 6 percent of SB polymer, these crosslinked products have a tendency to evolve, starting with the crosslinking that is carried out, and to polymerize completely during production or while in storage (forming a gelatinous mass). At this level of polymer concentrations, if the phenomenon of caking does not arise during production, viscosity will increase to such an extent that moving the asphalt: pumping and/or stirring, becomes impossible. In practical terms, these kinds of binders that are close to the state of gelling have difficulty mixing with other asphalts and cannot wet mineral or artificial surfaces in order to coat them.
In both these cases, this condition of instability has significant economic implications due to the loss of product or the neutralization of tanks and, aside from the risks that are incurred, clearly indicates the limits to the use of the discontinuous batch process for modified asphalts.
In order to solve all of the problems mentioned above, the applicant has found that, just after the direct injection of the sulfur-asphalt component or the polymer-asphalt mixture, the reaction took place very quickly and was irreversible, thereby helping to ensure that these types of crosslinked polymer asphalts acquired and immediately exhibited all of their characteristics. The use in practice of this new type of process, which makes it possible to mix all of the components just before the crosslinked binder has to be used, offers a broad range of possible uses that were previously unimaginable.
Up until now, the production of crosslinked polymer asphalts has been done using a discontinuous process. The principle of this process was: into a heated and stirred reactor are introduced, while being stirred, along with the amounts required for the formulation, in succession the necessary asphalt and then, over a relatively long period of time, depending on the amount to be employed, the polymer, optionally with the use of a liquid-solid grinder, which helps to speed up the dissolution of the solid and, if necessary, additives. When the mixture appears to be sufficiently homogeneous, sulfur or any other molecule that is able, by thermal decomposition, to produce it is incorporated, taking great care to ensure that the solid, at the instant that it makes contact with the surface of the medium, is immediately drawn completely into mixture. For a binder that contains between 3 and 4 percent polymer, it takes 6-7 hours to produce such a product, with a phase of at least two hours between the time when the sulfur begins to be introduced and stirring is finished and the binder is transferred to storage.
With the new process provided by the invention, depending on the application and the amount of polymer that has to be introduced, it will be necessary to prepare a SB polymer-asphalt concentrate, a mixture of the physical type, from asphalts with a penetration of between 60/70 (0.01 mm) and 600/800 (0.01 mm), and polymers such as styrene-butadiene, styrene-butadiene-styrene, styrene-isoprene, and styrene-isoprene-styrene. Preferably 200/500 (0.01 mm) penetration asphalts will be used to which 10-30 percent polymer, preferably of the styrene-butadiene type, can be added whose molecular weight will be between 55,000 and 95,000 grams. After it is dissolved, this product will represent the base concentrate of polymer asphalt. At the site where it is used, depending on the intended use, it will be necessary to prepare at least one second asphalt component that contains the chemical reagent, preferably a sulfur or a sulfur donor, to be selected from among molecules of such as polysulfides, etc. The asphalt will be selected from among asphalts with a penetration of between 10/20 (0.01 mm) and 180/200 (0.01 mm). The amount of sulfur or equivalent sulfur released by the donor agent will be between 1 and 15 percent. Depending on what is needed, it will also be possible to produce a third base that contains other polymers of virgin quality or polymers obtained from recycling, such as polyethylene or polypropylene or vinyl acetate or vinyl chloride or polyurethane, etc., or recycled rubber from tires. The asphalt will be preferably selected from among wet, high-penetration asphalts. The polymer concentration will depend on the type of types of polymers used. Depending on compatibility, the concentration may be between 5 and 15 percent relative to the asphalt, and then surface-agent chemical additives (polyamines, organic fatty acids) may also be introduced.
The facility will include the following items of equipment: injection pumps, mass flow counters, controlled and regulated valves, temperature indicators, and non-return valves. All of this is connected by pipes that are laid out with hot oil and are connected to the different tanks. All of these pipes empty at the inlet/feed of an in-line mixer that can be of different types: a static mixer or a chamber with dynamic stirrers. Preference will be given to the static mixer, which is simple in design, and said mixer will be sized for the desired hourly production range and for the different viscosity values of the products that it will have to mix. Of course, the way in which the characteristics of the mixer are defined will influence the characteristics of the metering pumps and, in particular, their delivery pressure. Likewise, all of the tanks and all of the items of equipment will be kept at high temperature and will be adapted to the type of product being stored, i.e., between 140 and 250xc2x0 C. To the extent required, the various pumps will send into the mixer each basic mix:
base concentrate with the reagent polymer (SB);
a diluting agent with a sulfur reagent;
a mixture with other polymers and/or additives.
The in-line mixer, which is designed to thoroughly disperse all of the components on a continuous basis, will help to initiate the reaction between the components of the asphalt, sulfur, and the SB polymer, and then to promote their development, thereby making it possible to obtain at the outlet finished crosslinked concentrated polymer asphalt.
When it is ouput, the binder is sent directly to the application units, preferably by hooking up the outlet pipe, using the shortest connections possible, either to a coating center mixer coating unit or to the injection ramp of a drum of the xe2x80x9cdrum-dryer-kneader/coaterxe2x80x9d (TSM/E) type of a permanent or mobile coating center or of a drum of a coating center of the mobile hot recycling unit for coated road materials or to the inlet of a coating machine for manufacturing sealant sheets or complexes.
As an example, the process for producing a crosslinked asphalt with 12 percent SB polymer and 0.3 percent sulfur is indicated. Two mixtures are prepared: the first (A) is perfectly homogeneous and hot at 180xc2x0 C. and will be composed of 85 parts direct-distillation asphalts with a penetration of 350 (0.01 mm) with 15 parts of a two-block styrene-butadiene polymer in proportions of 25/75; the second mixture (B), which is kept at 160xc2x0 C., consists of 85-99.9 parts but preferably 98.5 parts of the same 350 (0.01 mm) penetration asphalts and 1-15 parts but preferably 1.5 parts dissolved sulfur. Two pumps, with enough delivery pressure to overcome the load losses for the entire circuit, will inject the two fluids separately into the feed head of the static mixer. The flow rate of each pump will be controlled by mass counters that act on the controlled electric valves. The temperatures of the mixtures will also be benchmarked and regulated. The two mixtures will then be injected at a ratio of 80 parts of (A) to 20 parts (B). The product obtained at the outlet of the mixer will immediately have all of the characteristics needed so that it can be used in a new application as a crosslinked asphalt with a final proportion of polymer of greater than at least 4% of the total and preferably with 12 percent polymer.
This invention has some extremely important advantages. It will make it possible to employ reinforced binders with polymer contents of more than 10 percent, up to 35 percent, in order to produce special coated materials for roads. The binders that are obtained from the discontinuous process would not make it possible to produce such materials. Thus, this invention opens the way to producing coated materials that have very good properties, which will result in coated materials that are intended to be put to new uses, whereby said materials will guarantee longer service lives for road structures:
reinforcing and flexible coated materials;
coated materials that drain very well (with a high degree of void  greater than 30 percent);
ultrafine coated materials, etc.
Moreover, the incorporation of molecules that are able to release sulfur as they undergo thermal breakdown and that are associated with vulcanization accelerators and/or inhibitors will make it possible to manipulate the kinetics of vulcanization by speeding up or slowing down the reaction that is induced by sulfur between the polymer and the asphalt. It will be possible to pre-program the speed of the reaction based on the components cited above, such that said reaction will take place instantaneously or progressively over time. There was no point in even trying this approach with the old discontinuous process!
At the same time, there is also the option of using the invention to direct the binder that comes from the mixer straight to the inlet of a colloid emulsion mill. Keeping the emulsion at temperature of greater than 50xc2x0 C. will make it possible to immediately ensure the dispersion of particles of an asphalt that has a high concentration of crosslinked polymers; this cannot even be imagined today for the binders that are obtained from the discontinuous process with the existing equipment. As a matter of fact, the extreme elasticity of the products that are produced by the discontinuous process represents a physical barrier to their dispersion in water. Today, owing to a lack of cutting energy for cleaving the chemical chains that are created by the crosslinking reaction, the technology for the fabrication of emulsions of modified and crosslinked asphalt can be applied only to binders that contain no more than four percent polymer.
Likewise, according to the invention it will be possible to produce binders with very high polymer concentrations as regeneration agents for old asphalts that are contained in old coated materials in roads and to take advantage of the capability of the crosslinking reaction, which is ensured by a sulfur-vulcanized polymer asphalt, to propagate to any other new or old natural asphalt, such as is claimed in Spanish patent application P 9601837. Enhancing the value of old coated materials by the technique of hot recycling consists in reproducing a new asphalt by reusing all of the old materials. Because of the fact that the old materials are reused, it goes without saying that there is economic significance to this technique. In order to ensure that the recycled coated material will have acceptable characteristics, it is necessary to impart to the old asphalts properties that are at a level that is at least equivalent to, if not superior to those that said material originally possessed. The implementation of this technology runs into a physical limit corresponding to the total asphalt concentration. The new recycled coated material may not exceed a certain limit because too much binder can, in the road layer where it is used, create problems such as rutting. The need to fulfill this criterion limits the development of the interesting area of recycling to the economic sphere, i.e., between 80 and 100 percent of the material. The initial quantity of asphalt contained in a material to be regenerated is generally on the order of 5 percent or more; this leaves little room for a regenerating agent to be added (1.5 or even less than 1 percent). In view of the small quantities that can be used, it is clear that the formulation of such a regenerating agent must include such a large quantity of vulcanized polymer that there is no procedure today that would allow it to be produced. It is thus clear why there is significance to the invention, which makes it possible to produce a crosslinked, polymer-concentrated asphalt right at the time when this xe2x80x9cregenerating agentxe2x80x9d binder is introduced into the kneader or into the TSM/E. This technique requires that the materials be separated in advance so that they can be reheated advantageously. Under these conditions the regenerating agent, which is produced on the spot, is immediately brought to the injection ramp, and falls on the hot aggregate (160/190xc2x0 C.), will be dispersed evenly over the materials, and will integrate completely into the old asphalt, leading to the creation of the new binder. When installed on a hot recycling machine such as the ART (asphalt recycling travel plant) after certain steps are taken: division of the asphalt storage tank into various compartments, mounting of the platform for the fabrication team, etc., this same device produces the same results.
The sealant industry is also another example of an application for the invention. To produce complex sheets and sealing covers, this industry uses binders that are modified by high polymer concentrations. Because of the problems mentioned above, the mixtures that are created may not exceed 10 percent, and after these products are fabricated, they cannot be stored. Using the continuous production process would make it possible to continuously feed the coating machines, thereby eliminating the above-mentioned problems and at the same time taking advantage of the new levels of performance provided by these new binders.
The series of examples presented below illustrate the technical advantages that are offered by the various capabilities of the invention.